Removal of atmospheric pollutants from gas, related apparatus, processes and uses thereof

ABSTRACT

Methods related generally to the removal of atmospheric pollutants from the gas phase, are provided, as well as related apparatus, processes and uses thereof. A single-stage air scrubbing apparatus is provided that includes at least one reaction vessel, at least one introduction duct, and a turbulence component, wherein a residence time is sufficient to allow the conversion of at least one atmospheric pollution compound to at least one other compound, molecule or atom. In some embodiments, the at least one atmospheric pollution compound comprises nitrogen oxide, sulfur oxide or a combination thereof. Additionally, methods of removing atmospheric pollution compounds from a waste gas stream are disclosed that include introducing a waste gas stream and at least one additional gas stream, mist stream, liquid stream or combination thereof into a single-stage air scrubbing apparatus at a flow rate sufficient to allow for conversion of the at least one atmospheric pollution compound.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/715,149, filed Oct. 17, 2012, and U.S. Provisional Application No.61/715,146, filed Oct. 17, 2012, the disclosures of which are herebyexpressly incorporated by reference in their entirety and are herebyexpressly made a portion of this application.

FIELD

Methods related generally to the removal of atmospheric pollutants fromthe gas phase, are provided, as well as related apparatus, processes anduses thereof.

BACKGROUND

Atmospheric pollutants include those gases, particles, radicals andother molecules that make their way into the atmosphere from othersources or form in the atmosphere from the chemical reactions of othermolecules and energy sources. In general, atmospheric pollutants candamage the atmosphere by contributing to the “greenhouse effect”, bybreaking down the ozone layer, or by contributing to incidents of asthmaand breathing problems. These pollutants are not merely confined to theoutside, but can also be found in buildings. For example, many buildingshave loading docks near an air intake system. When a truck pulls up tothe loading dock, the truck exhaust can be pulled into the air intakesystem for a building and pollute the indoor air. There are also sourcesof atmospheric pollutants that originate from materials inside abuilding, such as carpet, paint, and commonly used chemicals.

Nitrogen oxides include a group of six compounds. Two members of thisgroup, nitrogen oxide (NO) and nitrogen dioxide (NO2), often referred toas NOx, are reactive species that are considered problematic atmosphericpollutants and that are subject to regulatory control. The gases areregulated because of the large quantities produced through combustionand other chemical reactions and because of their adverse effects inatmospheric chemistry. More than 2 million tons of NOx were generatedwithin the United States in 2011. Combustion typically produces 95% NOand 5% NO2. Nitric oxide, NO, is a significant reactive species in anatmospheric system, along with being present in several types of wastegases. It is the key component in the chain oxidation of organics, whichis brought about initially by the radical product of the reaction ofhydroxyl radical with organic compounds then adding an ozone molecule tothe open radical site. NO scavenges an oxygen atom from the radicalorganic species to form NO2. In ambient air, there are other importantmechanisms by which NO is quickly converted to NO2, including thefollowing (wherein R is an organic moiety):

2NO+O₂→2NO₂

k ^(298K)=2.0×10⁻³⁸ cm⁶ molecule⁻² s⁻¹

RO₂+NO→RO+NO₂

k ^(298K)=7.6×10⁻¹² cm⁶ molecule⁻² s⁻¹

HO₂+NO→OH+NO₂

k ^(298K)=8.3×10⁻¹² cm⁶ molecule⁻² s⁻¹

NO+NO₃→NO₂+O₂

k ^(298K)=1.8×10⁻¹⁴cm⁶ molecule⁻²s⁻¹

NO+NO₃→2NO₂

k ^(298K)=3.0×10⁻¹¹ cm⁶ molecule⁻² s⁻¹

A significant observation from the reactions above is that NO and ozonedo not reside in the same system in significant concentrations, since NOreacts with ozone quite rapidly comparatively. NO can also react with ROand OH radicals, which have been called “nighttime storage reactions”for NO. Those two reactions are effective until dawn, because HONO andRONO will rapidly photolyze when the sun rises. Researchers haveobserved that when benzene and NO are in the same system, there is adirect reaction between the two where a series of nitrophenols areformed.

The product of most of the NO reactions, NO2, is also responsible forseveral important reactions in the atmosphere. The first significantreactions for NO2 are its reaction with ozone to form nitrate radicaland oxygen or nitric oxide and two molecules of oxygen in reactions (14)and (15) below. This reaction is similar to the reaction of nitric oxideand ozone, in that neither molecule can simultaneously reside in theatmosphere in large concentrations. The nitrogen dioxide and ozonereaction has been attributed to the broad class of “nighttime chemistry”that NOx is responsible for in the atmosphere. NOx chemistry isimportant because many of its reactions do not require light, unlikeseveral of the oxygen reactions. Ozone concentration in the atmosphereis at its lowest at nighttime, and therefore, NOx species can interactwith other reactive species without automatically getting quenched byozone. The significant reactions of NO2 in the atmosphere are asfollows:

Reaction (13) is important environmentally because it is a source ofnitric acid in the troposphere. Nitric acid contributes significantly toacid rain and fogs during the daytime, since most of the hydroxylradical in the atmosphere is formed during daylight hours. Reactions(14) and (19) are chemically important because the highly reactivenitrate radical is formed.

Nitrate radical has been shown by researchers to be highly reactive,especially with organic compounds, such as simple alkenes and aldehydes.High nitrate radical concentrations have been spectroscopically observedin polluted urban areas. The primary time of day that the nitrateradical is most reactive is at night. The reaction of nitrate radicalwith the cresols and phenols is considered a significant sink for theseorganics at night. Nitric acid is formed in this reaction scheme, whichis an undesirable product in the atmosphere.

Research is currently being conducted to review NOx production in airsystems. One possibility for NOx compound formation is through thereaction of NNH and oxygen atoms. This scheme is as follows:

NNH

N₂+H  (24)

NNH+O₂

HNNOO

NNOOH→N₂+HO₂ or N₂O+OH  (25)

NNH+OH

HONH→N₂+H₂O  (26)

NNH+O

N₂+OH  (27)

NNH+O

N₂O+H  (28)

NNH+O

NH+NO  (29)

Reaction (24) shows the initial formation of NNH and is rapid on bothsides of the reaction leading to a quickly established equilibrium. OnceNNH is formed in the system, reactions (25)-(29) proceed at relativelyhigh rates of reaction. Therefore, there are new possibilities forgas-phase formation of NOx species in an air system.

Sulfur oxides (SOx) are compounds of sulfur and oxygen molecules. Sulfurdioxide (SO₂) is the predominant form found in the lower atmosphere. Itis a colorless gas that can be detected by taste and smell in the rangeof 1,000 to 3,000 micrograms per cubic meter (μg/m³). At concentrationsof 10,000 μg/m³, it has a pungent, unpleasant odor. Sulfur dioxidedissolves readily in water present in the atmosphere to form sulfurousacid (H₂SO₃). About 30% of the sulfur dioxide in the atmosphere isconverted to sulfate aerosol (acid aerosol), which is removed throughwet or dry deposition processes. Sulfur trioxide (SO₃), another oxide ofsulfur, is either emitted directly into the atmosphere or produced fromsulfur dioxide and is rapidly converted to sulfuric acid (H₂SO₄).

Most sulfur dioxide is produced by burning fuels containing sulfur or byroasting metal sulfide ores, although there are natural sources ofsulfur dioxide (accounting for 35-65% of total sulfur dioxide emissions)such as volcanoes. Thermal power plants burning high-sulfur coal orheating oil are generally the main sources of anthropogenic sulfurdioxide emissions worldwide, followed by industrial boilers andnonferrous metal smelters. Emissions from domestic coal burning and fromvehicles can also contribute to high local ambient concentrations ofsulfur dioxide.

Sulfur dioxide is a major air pollutant and has significant impacts uponhuman health. In addition the concentration of sulfur dioxide in theatmosphere can influence the habitat suitability for plant communitiesas well as animal life. Sulfur dioxide emissions are a precursor to acidrain and atmospheric particulates. Due largely to the US EPA's Acid RainProgram, the U.S. has witnessed a 33% decrease in emissions between 1983and 2002. This improvement resulted in part from flue-gasdesulfurization, a technology that enables SO₂ to be chemically bound inpower plants burning sulfur-containing coal or oil. In particular,calcium oxide (lime) reacts with sulfur dioxide to form calcium sulfite.Aerobic oxidation of the CaSO₃ gives CaSO₄, anhydrite. Most gypsum soldin Europe comes from flue-gas desulfurization. Sulfur can be removedfrom coal during the burning process by using limestone as a bedmaterial in Fluidized bed combustion. Sulfur can also be removed fromfuels prior to burning the fuel. This prevents the formation of SO₂because there is no sulfur in the fuel from which SO₂ can be formed. TheClaus process is used in refineries to produce sulfur as a byproduct.The Stretford process has also been used to remove sulfur from fuel.Redox processes using iron oxides can also be used, for example, Lo-Cator Sulferox. Fuel additives, such as calcium additives and magnesiumoxide, are being used in gasoline and diesel engines in order to lowerthe emission of sulfur dioxide gases into the atmosphere. As of 2006,China was the world's largest sulfur dioxide polluter, with 2005emissions estimated to be 25.49 million tons. This amount represents a27% increase since 2000, and is roughly comparable with U.S. emissionsin 1980.

Sulfur dioxide is the product of the burning of sulfur or of burningmaterials that contain sulfur:

S₈+8O₂→8SO₂

The combustion of hydrogen sulfide and organosulfur compounds proceedssimilarly.

2H₂S+3O₂→2H₂O+2SO₂

The roasting of sulfide ores such as pyrite, sphalerite, and cinnabar(mercury sulfide) also releases SO₂:

4FeS₂+11O₂→2Fe₂O₃+8SO₂

2ZnS+3O₂→2ZnO+2SO₂

HgS+O₂→Hg+SO₂

4FeS+7O₂→2Fe₂O₃+4SO₂

A combination of these reactions is responsible for the largest sourceof sulfur dioxide, volcanic eruptions. These events can release millionsof tons of SO₂.

Sulfur dioxide is also a by-product in the manufacture of calciumsilicate cement: CaSO₄ is heated with coke and sand in this process:

2CaSO₄+2SiO₂+C→2CaSiO₃+2SO₂+CO₂

The action of hot sulfuric acid on copper turnings produces sulfurdioxide.

Cu+2H₂SO₄→CuSO₄+SO₂+2H₂O

Sulfite results from the reaction of aqueous base and sulfur dioxide.The reverse reaction involves acidification of sodium metabisulfite:

H₂SO₄+Na₂S₂O₅→2SO₂+Na₂SO₄+H₂O

Treatment of basic solutions with sulfur dioxide affords sulfite salts:

SO₂+2NaOH→Na₂SO₃+H₂O

Featuring sulfur in the +4 oxidation state, sulfur dioxide is a reducingagent. It is oxidized by halogens to give the sulfuryl halides, such assulfuryl chloride:

SO₂+Cl₂→SO₂Cl₂

Sulfur dioxide is the oxidizing agent in the Claus process, which isconducted on a large scale in oil refineries. Here sulfur dioxide isreduced by hydrogen sulfide to give elemental sulfur:

SO₂+2H₂S→3S+2H₂O

The sequential oxidation of sulfur dioxide followed by its hydration isused in the production of sulfuric acid.

2SO₂+2H₂O+O₂→2H₂SO₄

Carbon bed adsorption, or adsorption by another material, is a processthat does not convert the components of waste gases to other compoundsas part of the process. Adsorption is an effective way of reducing theconcentration of components in a waste gas stream at a low flow rate.

The contaminated gas flows through the bed, where the components of thewaste gas can be adsorbed onto the bed material. There are, however,several problems with carbon bed adsorption. First, the choice of thebed material is one of the critical factors in the success of thecomponent removal. Activated carbon, molecular sieves, activatedalumina, and activated silica are common bed materials, althoughactivated carbon is commercially the material of choice. The compositionof the bed material influences which waste gas component is adsorbed andwhich components pass through the system and into the outlet air stream.Therefore, it is helpful if the operator knows the contaminants of theair sample that is being cleaned.

Second, the adsorption technique does not break down the components ofthe waste gas into smaller and/or other compounds; it only collects themon the bed material. Once the bed becomes saturated, it is taken offline and cleaned. The cleaning process can involve simply steam cleaningthe bed, or regeneration, or can involve using a solvent combined withsteam cleaning to remove captured waste gas components. The wasteproducts from this process are then collected and disposed of by anenvironmentally safe procedure. The most common procedure is to separatethe waste gas components from the aqueous phase that was produced by thesteam cleaning process. This is time consuming, labor intensive andcostly.

Another problem with the adsorption technique is that it requires morethan one bed in parallel and sometimes in series. The adsorption processrequires beds in parallel so that when one bed becomes saturated, it canbe taken off line and the other bed put into subsequent use. Sometimes,it becomes advantageous to put beds in series so that largeconcentrations of waste gas components can be removed. The operator canalso put beds made of different material in series to target differentcombinations of waste gases. These adsorption beds are quite bulky,since their average depth is one to three feet, therefore this processcan be undesirable if space is limited. The arrangement of beds inseries and parallel add to the consumption of time, labor and money incooling and cleaning of the waste and the bed material.

Absorption is the process by which part of a gas mixture is transferredto a liquid based on the preferential solubility of the gas in theliquid. This process is used most often to remove acid stack gases, butit is a complex and costly method of control and removal of othercomponents of waste gases. The high cost of the process is based on thechoice of the absorbent and the choice of the stripping agent.Absorption is limited in its utility and not widely implemented in smallindustrial settings.

Plasmas are electrical discharges that form between electrodes. Thereare five general classes of nonequilibrium plasmas that can be used insome capacity for chemical processing, including synthesis anddecomposition: the glow discharge, the silent discharge, the RFdischarge, the microwave discharge, and the corona discharge. Each classis specific based on the mechanism used for its generation, the range ofpressure that is applicable during its use, and the electrode geometry.

While electrical discharges are effective in breaking down components ofwaste gases into other compounds and components, it is clear that ineach of these discharge arrangements, they require a power source (insome cases a significant one), may not be able to handle industrialscale treatment without honeycombed and serial designs of thedischarges, and are generally designed to combat complicated waste gasstreams that comprise various components, including ozone, NOx andvolatile organic compounds.

Wet scrubbing methods are conventionally employed for removal ofparticulates, SOx and NOx from waste gas streams. For waste gas streamsthat contain a significant amount of NOx, whether it was an originalcontaminant or the result of chemical conversion of a volatile organiccomponent, conventional technologies, such as those described earlier,may not be able to efficiently handle the NOx load on an industrialscale. Conventional technologies for industrial scale NOx treatmenttypically treat the NOx with two or three stage wet scrubbingtechnologies. The most common currently used is a three stage process:Stage 1 converts NO into NO₂. Stage 2 chemically transforms the NO₂ intoother nitrogen containing compounds. Stage 3 removes odors created inthe second stage. Literature shows a number of chemical reactants, someof which were outlined earlier, that are utilized in this and othermulti stage NOx treatment technologies. These include nitric acid andhydrogen peroxide, sodium hydrosulfide and hydrogen peroxide, or ozonegas and sodium chlorite solution, ferric salt solutions and others. Allof these are relatively effective, but each has pronounced limitationsin operating costs, equipment costs or removal efficiency.

Conventional research has described chlorine dioxide's ability toconvert NO into NO₂, which has typically been described in literature asoccurring in a wet scrubbing apparatus according to equation 30 below.Researchers in this area also describe the use of sodium chlorite inwater solution within a packed bed or tray type scrubbing or other wetscrubbing apparatus to convert NO₂ into nitric and hydrochloric acid asdescribed in equation 31 below.

2NO+ClO₂+H₂O→NO₂+HNO₃+HCl  (30)

4NO₂+NaClO₂+2H₂O→4HNO₃+NaCl  (31)

As shown in many of these conventional applications where waste gasvolumes are small, NOx and SOx can be adsorbed on carbon and otherporous solid materials or absorbed into liquids like sodium hydroxideand water. Although useful in small volume applications, thetechnologies are not economically practical for industrial applicationsthat produce tens of thousands of cubic feet per minute of waste gascontaining NOx and SOx. Catalysts provide another technical option; theycan reduce NOx into nitrogen compounds that are not consideredpollutants. Catalysts are effective on gas streams with small oxygenconcentrations. Unfortunately most industrially produced NOx waste gasstreams also contain high oxygen concentrations, so this technology isnot applicable.

Methods known in the art for abating nitrogen oxides using, e.g.,chlorine dioxide, include those of U.S. Pat. No. 4,119,702 to Azuhata etal., U.S. Pat. No. 3,957,949 to Senjo et al., and U.S. Pat. No.3,023,076 to Ernst Karwat.

SUMMARY

Accordingly, it would be desirable to develop, produce and utilize anapparatus and related process that converts NOx and/or SOx in a wastegas stream to other compounds, molecules or atoms, wherein the apparatusand process achieves one or more of the following goals: a) can operateon an industrial scale, b) does not require significant amounts ofenergy from outside sources, c) can process waste gases in the gas phasewith low, medium and high amounts of humidity (including liquid and/oraqueous phase materials), d) can process waste gases in the liquid oraqueous phase, e) is cost efficient relative to the scale of theprocess, f) is generally easy to install and operate, and g) caneffectively operate as a single stage unit.

Current methods of cleaning air, such as catalytic oxidation,condensation, absorption, and carbon bed adsorption, are in generalbulky, expensive, and maintenance intensive. Therefore, a process thatcould minimize these problems found with the currently used methodswould be a beneficial next step in the development of better technologyfor air quality control. An ideal process can control low concentrationsNOx in air, as well as successfully controlling larger concentrations ofNOx that are present in the same air sample.

A single-stage air scrubbing apparatus is disclosed that includes: atleast one reaction vessel having a first end, a second end, anenclosure, comprising at least one wall, a volume within enclosure and aresidence time component, at least one introduction duct that is coupledto the reaction vessel, and a turbulence component, wherein theresidence time component is sufficient to allow the conversion of atleast one atmospheric pollution compound to at least one other compound,molecule or atom. In some embodiments, the at least one atmosphericpollution compound comprises nitrogen oxide, sulfur oxide or acombination thereof.

Additionally, methods of removing atmospheric pollution compounds from awaste gas stream are disclosed that include: providing a single-stageair scrubbing apparatus, providing a waste gas stream having at leastone atmospheric pollution compound, providing at least one additionalgas stream, mist stream, liquid stream or combination thereof,introducing the waste gas stream and the at least one additional gasstream, mist stream, liquid stream or combination thereof into thesingle-stage air scrubbing apparatus at a flow rate sufficient to allowfor conversion of the at least one atmospheric pollution compound to atleast one other compound, molecule or atom, and converting the at leastone atmospheric pollution compound to at least one other compound,molecule or atom.

In a first aspect, a method is provided for scrubbing a waste gas,comprising, introducing into a reaction vessel a waste gas containing atleast one component selected from the group consisting of a sulfur oxideand a nitrogen oxide; introducing chlorine dioxide into the reactionvessel; introducing turbulence into a mixture of the waste gas and thechlorine dioxide, whereby the chlorine dioxide reacts with thecomponent, such that the component is converted into at least one othercompound, molecule or atom.

In an embodiment of the first aspect, the chlorine dioxide is in gaseousform.

In an embodiment of the first aspect, the chlorine dioxide reacts withthe component under conditions of ambient temperature and ambienthumidity.

In an embodiment of the first aspect, the chlorine dioxide is introducedinto the reaction vessel via at least one introduction duct.

In an embodiment of the first aspect, turbulence is introduced bypassing at least one of the waste gas and the chlorine dioxide through aset of two or more blades in a fan configuration.

In an embodiment of the first aspect, turbulence is introduced bypassing at least one of the waste gas and the chlorine dioxide through aplurality of tubes arranged in a parallel configuration, wherein eachtube is positioned at an angle of from 5 to 95 degrees off an axis ofthe reaction vessel, and wherein each tube is less than 0.5 meters inlength.

In an embodiment of the first aspect, the mixture is passed through twoor more reaction vessels arranged in series.

In an embodiment of the first aspect, a sensor for detection of at leastone of the component, compound, molecule, or atom is positioned at anexit from the reaction vessel, and wherein a measurement by the sensoris employed to adjust an amount of at least one of the waste gas andchlorine dioxide in the mixture so as to increase a rate and/or anamount of reaction of the component.

In an embodiment of the first aspect, a residence time of the mixture inthe reactor is 1.5 seconds or less, and wherein a conversion of thecomponent of at least 99% is achieved.

In a second aspect, a system is provided for scrubbing a waste gas of atleast one of nitrogen oxides and sulfur oxides, comprising: an inlet forintroducing chlorine dioxide into the reaction vessel; and an inlet forintroducing waste gas into the reaction vessel; and a reaction vessel,wherein the reaction vessel is equipped with one or more turbulenceinducing devices for inducing turbulence in a mixture of the waste gasand the chlorine dioxide.

In an embodiment of the second aspect, the system further comprises atleast one sensor positioned in an outlet of the reaction vessel, whereinthe sensor is configured to measure at least one of sulfur oxide,nitrogen oxide, water, or temperature.

In an embodiment of the second aspect, the reaction vessel is configuredsuch that a residence time of a 1.5 seconds or less.

In an embodiment of the second aspect, the turbulence inducing device isselected from the group consisting of vanes, baffles, diffusers, andtube arrays.

In an embodiment of the second aspect, the system further comprises atleast one additional reaction vessel, wherein the reaction vessels arearranged in series.

In an embodiment of the second aspect, a gas velocity of the mixture isless than about 2500 feet per minute

In a third aspect, a single-stage air scrubbing apparatus is provided,comprising: at least one reaction vessel having a first end, a secondend, an enclosure, comprising at least one wall, a volume withinenclosure and a residence time component, at least one introduction ductthat is coupled to the reaction vessel, and a turbulence component,wherein the residence time component is sufficient to allow theconversion of at least one atmospheric pollution compound to at leastone other compound, molecule or atom.

In an embodiment of the third aspect, the at least one atmosphericpollution compound comprises nitrogen oxide, sulfur dioxide or acombination thereof.

In an embodiment of the third aspect, the at least one reaction vesselcomprises two or more reaction vessels in series with one another.

In an embodiment of the third aspect, the at least one reaction vesselcomprises two or more reaction vessels in parallel with one another.

In an embodiment of the third aspect, the air comprises gas, mist,liquid or a combination thereof.

In an embodiment of the third aspect, the at least one introduction ductis coupled to the first end, the second end, the at least one enclosureor a combination thereof.

In an embodiment of the third aspect, the reaction vessel has a circularcross-section, an oval cross-section, a triangular cross-section, arectangular cross-section, a square cross-section or a combinationthereof.

In an embodiment of the third aspect, the residence time component isgreater than about 0.1 second.

In an embodiment of the third aspect, the residence time component isgreater than about 0.5 second.

In an embodiment of the third aspect, the residence time component isgreater than about 1.5 seconds.

In an embodiment of the third aspect, the at least one nitrogen oxidecompound comprises nitric oxide, nitrogen dioxide or a combinationthereof.

In a fourth aspect, a method is provided of removing atmosphericpollution compounds from a waste gas stream, comprising: providing asingle-stage air scrubbing apparatus, providing a waste gas streamhaving at least one atmospheric pollution compound having a velocity,providing at least one additional gas stream, mist stream, liquid streamor combination thereof having a velocity, introducing the waste gasstream and the at least one additional gas stream, mist stream, liquidstream or combination thereof into the single-stage air scrubbingapparatus at a flow rate sufficient to allow for conversion of the atleast one atmospheric pollution compound to at least one other compound,molecule or atom, and converting the at least one atmospheric pollutioncompound to at least one other compound, molecule or atom.

In an embodiment of the fourth aspect, the at least one atmosphericpollution compound comprises nitrogen oxide, sulfur dioxide or acombination thereof.

In an embodiment of the fourth aspect, the gas velocity is less thanabout 2500 feet per minute.

In an embodiment of the fourth aspect, the gas velocity is less thanabout 1000 feet per minute.

The various embodiments of the various aspects, as well as the variousaspects, can be employed in any suitable combination as desired.

BRIEF DESCRIPTION OF THE DRAWINGS

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

FIG. 1 shows the tendency to decompose as a function of % chlorinedioxide in air (based on technical bulletin by Basic Chemicals).

FIG. 2 shows a contemplated induction time, the time required fordecomposition of chlorine dioxide as a function of time and partialpressure.

FIG. 3 shows a plot of chlorine dioxide vapor pressure as % in air atvarious temperatures.

FIG. 4 shows a contemplated embodiment of an apparatus.

FIG. 5 is a photograph of a circular diffuser for introducing waste gasinto a reactor of a preferred embodiment.

FIG. 6 is a photograph showing a close up of the circular diffuser ofFIG. 6, including the arrangement of holes through which waste gas isintroduced into the reactor.

FIG. 7 is a photograph showing a reactor insert for introducingturbulence in the reactor.

FIG. 8 is a photograph showing a spinner spool for introducingturbulence in the reactor.

FIG. 9 shows a top view schematic diagram of a first spinner spool ofFIG. 8.

FIG. 10 shows a top view schematic diagram of a second spinner spool ofFIG. 8.

DETAILED DESCRIPTION

The following description and examples illustrate some exemplaryembodiments of the disclosed invention in detail. Those of skill in theart will recognize that there are numerous variations and modificationsof this invention that are encompassed by its scope. Accordingly, thedescription of a certain exemplary embodiment should not be deemed tolimit the scope of the present invention.

An apparatus and related processes have been developed that convertatmospheric pollution compounds, including NOx and/or SOx, in a wastegas stream to other compounds, molecules or atoms, wherein the apparatusand process may achieve one or more of the following goals: a) operateson an industrial scale, b) does not require significant amounts ofenergy from outside sources, c) processes waste gases in the gas phasewith low, medium and high amounts of humidity, d) processes waste gasesin the liquid or aqueous phase, e) is cost efficient relative to thescale of the process, f) is generally easy to install and operate, andg) effectively operates as a single stage unit, regardless of how manyreaction vessels are included.

Chlorine dioxide is a powerful oxidizing agent. Chlorine dioxide canreact with fluoride, fluoroamines, carbon monoxide, hydrogen, ammonia,phosphine, platinum, phosphorus, potassium hydroxide, ethane, propaneand methane. It reacts with steam or water to produce hydrochloric acid.Chlorine dioxide can react with NOx and SOx, making it useful forscrubbing waste gas containing these compounds. Contemplated embodimentsinclude processes and apparatus that remove NOx and SOx from industrialwaste gas or other gas that contains NOx (converts both NO and NO₂ intomineral acids) and/or SOx. Contemplated processes involve a chemicalreaction between chlorine dioxide gas (ClO₂) and the NOx in a singlestage air or mist type scrubbing apparatus. Contemplated processesutilize ClO₂ to remove NOx from industrial waste gas (or other gasescontaining NOx) in two ways: a) a reaction(s) between the NOx in thewaste gas and gaseous chlorine dioxide that is dissolved in a aqueoussolution, which may be at any suitable pH, including acidic, neutral orbasic, and b) a reaction between ClO₂ gas and NOx in a waste gas withhigh relative humidity. Both reaction types can proceed according to thepaths described in reaction (32) and (33) below, but contemplatedembodiments are not limited to any particular theory or presumedpathway. Both of these methods use a single stage air or mist scrubbingapparatus that is a major departure from the multi-stage wet scrubbingapparatus reported in prior art applications and utilizedconventionally.

Contemplated apparatus and related processes convert NOx gases intoother nitrogen containing compounds that are not considered pollutantsand/or convert SOx gases into other sulfur containing compounds that arenot considered pollutants. The technology of contemplated processestreats NOx and/or SOx more efficiently and with lower initial equipmentand/or operating costs than the prior art processes described above.Although the present process has broad technical application, it offersa profound and immediate improvement in the treatment of industriallycreated NOx and/or SOx waste gas. The present process is applicable toindustrial applications like chemically dissolving and pickling metals,stationary source combustion process flue gas, tail gas from nitric acidplants, shipboard combustion process flue gas and other sources of wastegas containing nitrogen oxides. This process efficiently treats NOxand/or SOx and is more cost effective to install and operate thancurrently available technologies for NOx and/or SOx treatment describedin other patents and literature.

Specifically, a single-stage air scrubbing apparatus is provided toaddress one or more of the problems outlined earlier and includes: areaction vessel having a first end, a second end, an enclosure,comprising at least one wall, a volume within the enclosure, and aresidence time component, at least one introduction duct that is coupledto the reaction vessel, and a turbulence component, wherein theresidence time component is sufficient to allow the conversion of atleast one nitrogen oxide and/or sulfur oxide compound to at least oneother compound, molecule or atom. For mist-based ClO₂ processes,residence times of about 0.15 seconds to 15 seconds, are generallypreferred, preferably 0.5 or 1 second to about 1.5, 2, 2.5, or 3seconds, with approximately 1.5 seconds generally preferred. Forgas-based ClO₂ processes, residence times of about 0.015 seconds to 1.5seconds, are generally preferred, preferably 0.05 or 0.1 seconds toabout 0.15, 0.2, or 0.3 seconds, with approximately 0.15 secondsgenerally preferred. However, in either mist or gas based processes,longer or shorter times can be employed in certain embodiments. Variousreactor configurations can be employed to obtain a desired residencetime in a particular apparatus footprint, depending upon constructionand spacing constraints. For example, the reactor can be positionedvertically, horizontally, or positioned diagonally at any desired anglebetween 0 and 90°. The velocity through which the waste gas and chlorinedioxide passes through the reactor can be varied, with faster velocitiesin longer reactors and slower velocities in shorter reactors. Thereactor can be of any suitable configuration, e.g., a straight tube, ahelical coil, a tortuous path provided by a series of baffles in acylindrical tube, a tube including a series of switchbacks, multipleparallel tubes, or any other suitable configuration. Pure waste gas canbe added to the reactor along with the chlorine dioxide, or the gasescan be diluted, e.g., with ambient air, or with inert gases, treated gasstreams, or other gas streams including untreated gas streams. While itis generally preferred to operate the reactor at ambient temperatures(temperatures typically experienced outdoors in the various regions ofthe United States, e.g., −40° C. or lower to 40° C. or higher, typically0° C. to about 25° C.), heating or cooling jackets for the reactor canbe employed, or other devices for heating or cooling gases introducedinto the reactor.

Good results derived from gas or mist phase scrubbing of NOx arediscussed herein. For example, greater than 99 percent of the NOx can beconverted to nitric acid and hydrochloric acid in approximately 1.5seconds of residence time when mixed with gas phase chlorine dioxide invery moist air, e.g. air at a relative humidity of approximately 100%,or containing liquid water in aerosol form (e.g., a mist). It istypically desirable to operate the reactor at ambient conditions ofhumidity. Such relative humidity levels can range from 2% or below inextremely dry conditions to 100% relative humidity in coastal areas.More typical relative humidities are as low as 10%, more typically30-60% for desert areas of the southwestern United States, to above 70%in non-desert areas. If higher moisture content is desired, then watercan be added in vapor or mist form. Additional research shows that mistand dissolved ClO₂ provide effective conversion of NOx in about 1.5seconds, and gas phase ClO₂ provide effective conversion of NOx in about0.15 seconds. Increasing humidity or moisture can sometimes slow thereaction time. As noted above, conversion of greater than 99 percent ofthe NOx can be achieved. Similar conversion levels may be obtained forSOx. In other embodiments, lower conversions of SOx and/or NOx may beacceptably obtained, e.g., 50% or less up to 55, 60, 65, 70, 75, 80, 85,90, 95, 96, 97, or 98%, or up to 99% or more. In certain embodiments,higher conversions may be obtained, e.g., 99.9%, or 99.99%, or 99.999%or more. Although a single pass reactor is typically preferred, serialreactors can advantageously be employed to provide higher conversionlevels.

Good results are also seen when chlorine dioxide gas is dissolved insodium hydroxide solution or other basic solutions with pH above 9, andintroduced into the reactor in the form of a mist; however, with theappropriate chemistry considerations, a basic pH is not necessary foreffective conversions of atmospheric pollutants. It is instructive tonote that the solution pH is multifaceted issue. A high pH is notnecessary for the some of the contemplated chlorine dioxide reactionsshown here. In fact, chlorine dioxide decomposes in high pH. Therefore,it is important that the chlorine dioxide is exposed to high pH for onlya limited period of time. Fortunately, the chlorine dioxidedecomposition rate is sufficiently slow that it allows a high pHreaction environment for the second or two necessary to decompose theNOx. A higher pH is introduced from OH⁻, for example, because thisenvironment converts the NO₂ into innocuous compounds. Sodium hydroxideis considerably less expensive than chlorine dioxide and its presencereduces the overall chemical cost in NOx destruction. There are severalcontemplated methods of introducing a high pH into the process. One isto insure the high pH liquid is introduced into the reaction chamberalong with the chlorine dioxide gas. The second is to mix it with theliquid-containing dissolved chlorine dioxide just prior to injectioninto the reaction chamber. In a single mist scrubbing stage, NOxconcentrations between 10 and 100 ppm containing both NO and NO₂ wereconverted to the acids. An optional second stage mist or wet scrubbingapparatus provides additional gas cleaning. This second stage can bedesigned to capture excess chlorine dioxide and/or acid fumes. Whileconcentrations of from 10-100 ppm of NOx are desirably treated, incertain embodiments higher or lower concentrations may also be treated,e.g., from 1 ppm or less to 1000 ppm or more.

While single stage reactors are typically preferred, more than onereactor of preferred embodiments in series can be employed to achievehigher conversion rates (e.g., 2, 3, or more reactors in series).Multiple reactors of preferred embodiments in parallel can be employedto provide compact conversion of higher volumes of waste gas. A singlestage reactor of a preferred embodiment can also be employed inconnection with one or more other types of conventional reactors asdescribed above, either for first pass removal of NOx and/or SOx or asan intermediate or final treatment step.

In another embodiment, at least one atmospheric pollutant can beeffectively converted by scrubbing with gas phase ClO₂ in waste gas withambient humidity and ambient temperatures as described elsewhere herein,and then direct the exit gas into a second stage scrubber thatrecirculates NaOH (or another basic compound). This second stage treatsany remaining NO₂ and captures any extra ClO₂. The captured ClO₂ isuseful in the treatment of NOx too. Furthermore, when the ClO₂ isgenerated using an electrochemical device, the effluent from the cellscan be utilized in the second scrubbing stage to minimize the additionof NaOH so as to reduce operating costs.

Additionally, methods of removing atmospheric pollution compounds from awaste gas stream are disclosed that include: providing a single-stageair scrubbing apparatus, providing a waste gas stream having at leastone atmospheric pollution compound, providing at least one additionalgas stream, mist stream, liquid stream or combination thereof,introducing the waste gas stream and the at least one additional gasstream, mist stream, liquid stream or combination thereof into thesingle-stage air scrubbing apparatus at a flow rate sufficient to allowfor conversion of the at least one atmospheric pollution compound to atleast one other compound, molecule or atom, and converting the at leastone atmospheric pollution compound to at least one other compound,molecule or atom.

In contemplated embodiments, NOx-containing gas and/or SOx-containinggas (which are referred to herein as “waste gas” or “gas” or even attimes “waste air”) is streamed through a vessel at a suitable gasvelocity for conversion and scrubbing waste gas. In some contemplatedembodiments, a contemplated gas velocity is less than about 2500 feetper minute. In other contemplated embodiments, a contemplated gasvelocity is less than about 2000 feet per minute. In yet othercontemplated embodiments, a contemplated gas velocity is less than about1500 feet per minute. In some contemplated embodiments, a contemplatedgas velocity is less than 1000 feet per minute. Gas velocities of from100 feet per minute or less to 5000 feet per minute or more can beemployed. With these contemplated gas velocities, it is expected that acontemplated residence time of gas in the vessel is typically about 0.1seconds or more to about 1.5 seconds or less, although in certainembodiments higher or lower residence times can be employed.

Contemplated reaction vessels are constructed of materials that aresubstantially impervious or resistant to reaction the waste gas and havea volume sufficient to contain the waste gas stream for a period of notless than about 0.1 second, and in many embodiments, not less than about1.5 seconds. Suitable materials that can be employed for the reactorinclude PVC, fiberglass, steel, ceramic, and various compositematerials. Contemplated reaction vessel designs may be any shape andcomprise at least one wall. In some embodiments, a contemplated reactionvessel is cylindrical (having a circular cross-section profile) becausethis shape minimizes interference between the gas and the vessel walls.However, any reaction vessel design that allows for the possibility offormation of very small liquid droplets and minimal coalescing ofmoisture within the reaction chamber is contemplated, even if it is notcylindrical. It is preferably understood that there are embodimentswhere liquid droplets and moisture do not form, however, thesecomponents are preferably designed to withstand and address manydifferent types of waste gases, treatment conditions and resultingcomponents. Therefore, if the design considerations are reviewed toprovide sufficient residence time, along with a lack of moisturecoalescence, then any design may be used, including rectangular, oval,triangular, conical or a combination thereof.

As mentioned, contemplated apparatus comprise at least one introductionduct that is coupled to the reaction vessel. A contemplated waste gas issupplied or provided to the point of introduction to the reaction vesselthrough this at least one duct. The orientation of the duct is can beadjusted as desired to improve performance. In certain embodiments,performance can be enhanced by minimizing the interference between thegas and the vessel walls. Contemplated orientations include: a) at thecenter of the end of a cylindrical vessel, or b) at the side andtangentially aligned with circumference of a cylindrical vessel.

As previously discussed, contemplated embodiments also comprise aturbulence component. Contemplated turbulence components may compriseany single design or combination of designs wherein the turbulencecomponent functions to introduce gas mixing by providing a swirl orturbulence to the waste gas or gas stream. In contemplated embodiments,the turbulence component is located such that it can add turbulence ormixing to the waste gas or gas stream before the gas comes into contactwith the chlorine dioxide or when chlorine dioxide is introduced into amist or liquid. When ClO₂ is introduced as a gas the mixing can occurbefore, during and/or after the ClO₂ is introduced, or before, duringand/or after the ClO₂ is added to the gas stream containing NOx and/orSOx. ClO₂ can be added to the waste gas and/or the waste gas can beadded to ClO₂. Waste gases of different compositions can be combined invarious combinations with ClO₂ in various sequences, as desired.

FIGS. 5-6 are directed to a circular device for introducing gas into thereactor. The device includes a ring of PVC pipe with ends connected viaa T-shaped connector. Gas is introduced into the T-shaped connector anddiffuses out through a plurality of holes in the walls of the pipe (seedetail in FIG. 6).

FIG. 7 is directed to a device for introducing turbulence into thereactor. The device includes a bundle of short, small diameter PVC pipelengths tilted at an angle to an axis of a sheath fabricated from alarge diameter PVC pipe. The short, small diameter PVC pipe lengths aretypically from about 2 inches in length or less to 12 inches in lengthor more, e.g., from 2, 3, 4, 5, or 6 to about 7, 8, 9, 10, 11 or 12inches. Diameters are typically uniform, and from about 0.5 inches orless to about 2 inches or more, e.g., 0.5, 0.75, or 1 inch to about1.25, 1.5, or 2 inches. The pipes are typically tilted off of the axisfrom 5 or less to 85 or more degrees, typically from about 5, 10, 15,20, or 25 degrees to about 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80,or 85 degrees. The tilted pipes are preferably arranged in a spiralpattern so as to maximize generated turbulence. The sheath typically hasa diameter that facilitates placing the device in the flow path of thereactor, e.g., as a pipe forming a portion of the length of a reactor,or as an insert into the reactor having a diameter sufficiently smallsuch that it can be inserted into the larger diameter reactor, butsufficiently large so as to provide a snug fit to encourage passage ofsubstantially all gas therethrough. The device can be fabricated fromany suitable material capable of tolerating exposure to the waste gasand chlorine dioxide.

FIGS. 8-10 are directed to spinner spools for introducing turbulenceinto the reactor. The blades of the spinner spool are tilted at an angleof 30 degrees; however, other angles such as are described above withrespect to FIGS. 6-7 can be employed. Any suitable number of vanes canbe employed, e.g., 2 to 30 or more, preferably, 3, 4, 5, 6, 7, 8, 9, or10 to about 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,26, 27, 28, 29, or 30.

While the configurations of FIGS. 6-10 are desirable for inducingturbulence in many configurations, other configurations can also beemployed, e.g., screw shaped blades, baffles, plates with holes, etc.For energy conservation and robustness of equipment, stationary devicesfor inducing turbulence are particularly desired; however, moving fans,blowers, mixers, and the like may also be employed in certainembodiments.

In some embodiments, when the waste gas is introduced at the center ofthe end of a cylindrical reaction vessel, a contemplated turbulencecomponent is placed in the duct just prior to the point where the gasenters the vessel, or it may be placed at the beginning of the vesseljust after the waste gas enters the vessel or the reaction can occur inthe duct with no need for a reaction vessel. Multiple turbulencecomponents can be employed, spaced evenly or irregularly along thereaction vessel, e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, or more. The waste gas and/or the ClO₂ can be introduced via oneinlet, or a plurality of inlets, e.g., 5, 10, 20, 30, 40, 50, or 100 ormore inlets, of various spacings and configurations. The waste gasand/or ClO₂ can be introduced in undiluted (or pure) form, or mixedwith, e.g., air, inert gas (e.g., argon, nitrogen or CO₂), water, or thelike, or with another reactive component. The configuration of thevessel can be adjusted to account for the moisture associated with theClO₂ when it is introduced into the reaction vessel. In othercontemplated embodiments, when the waste gas is introduced at the sideand tangentially aligned with circumference of a cylindrical reactionvessel, a contemplated turbulence component is located at a position toswirl or mix the gas in the duct just prior to the point where the wastegas enters the vessel. In other contemplated embodiments, if arectangular or other reaction vessel configuration is used, then theturbulence component preferably minimizes collision between the vesselwalls and gas turbulence within the reaction vessel when the ClO₂ isintroduced in a mist or liquid phase.

In embodiments where the chlorine dioxide is dissolved in a liquid,e.g., water, a chlorine dioxide fluid material or aqueous material issprayed, released or propelled into the waste gas stream. Incontemplated embodiments, the chlorine dioxide fluid material issprayed, released or propelled a point just downstream of the point atwhich the gas is swirled by the turbulence component, and in manyembodiments, through a single nozzle. In some contemplated embodiments,a reaction vessel comprises a single nozzle for this purpose that islocated just downstream of the point where the gas is swirled. However,in other embodiments, such as where non-cylindrical reaction vessels areutilized, it may be desirable to utilize multiple nozzles. In caseswhere multiple nozzles are used, it may also be beneficial for the gascoming out of each nozzle to spin in opposite directions. In thesecases, gas mixing is optimized and gas turbulence is minimized.

In contemplated embodiments, the nozzle orientation is centered with theaxis of the gas flow and provides a full cone or other full surfacepattern that evenly disperses the material projected from the nozzleinto the entire waste gas stream. In contemplated embodiments, the rateof release from the nozzle may be calibrated so that it is at leasttwice the velocity of the waste gas stream. When the nozzle is emittinga liquid it preferably produces droplets of that liquid with a meandiameter of about 100 microns or less. In these instances, it isimportant to remain below the dew point of the gas, and thereby preventformation of liquid droplets, especially those with a larger meandiameter.

Contemplated liquids may be formed from a condensed spray, but may alsobe formed from other methods and/or apparatus. Contemplated liquidscould, and usually would, contain high concentrations of HCl and HNO₃.Therefore, contemplated reaction vessels may comprise a drain at a lowpoint in the vessel to allow the removal of that liquid. In someapplications, depending upon other contaminants in the waste gas and thepH of the moisture (fluid material) added to the waste gas, thiscondensate acid mix can be of commercial value.

When chlorine dioxide gas in introduced into a waste stream, it ispreferably introduced in stoichiometric excess for reaction withcomponents to be reacted, e.g., SOx and NOx. For example, the chlorinedioxide can be present in concentrations or amount or levels greaterthan merely sufficient to react with the NOx as set forth in equations32 & 33 below). It is understood, however, that the chlorine dioxide ingaseous form is neutral, meaning that it is not the ionic ClO₂ ⁻ that isformed when NaClO₂ is dissolved in water. The ionic form is useful forNO₂ conversion into acids, but is not useful in the conversion of NO toNO₂.

In some contemplated embodiments, the ClO₂ gas is generated on site andintroduced (sprayed) into the waste gas through one or more nozzlesdescribed above, as either a liquid or gas. Liquid has advantages and isused in some embodiments unless the NOx concentration in the waste gasrequires more ClO₂ than can be safely dissolved into an aqueoussolution. And the waste gas humidity is sufficiently low to allow theintroduction of liquid without exceeding 100% humidity. The dissolvedClO₂ gas concentration in aqueous solutions typically should not exceed3000 ppm for safety reasons, but systems may be designed such that thisconcentration can be safely exceeded.

The stability of chlorine dioxide includes three primary variables:temperature, pressure and concentration. The parameters have beenstudied systematically by Ri Ya Jin et al and Basic Chemical Inc., andothers, which make the point that there are a number of safe operatingenvironments for chlorine dioxide. It is possible to safely utilizechlorine dioxide in the NOx scrubbing technology disclosed herein for avariety of industrial and municipal waste gas environments withsignificantly varied combinations of temperature and NOx concentration.This does not mean that chlorine dioxide will not decompose to chlorineand oxygen below 9.5% in air. But the induction time is in severalminutes as FIG. 2 shows.

There are three operational environments to consider when evaluating thesafety and chemical availability of chlorine dioxide: gas storage, gastransport to reaction chamber, and within the reaction chamber. Each ofthese can be different. For example, it is only necessary to have thechlorine dioxide remain intact long enough within the reaction chamberto complete the desired reaction.

Several studies have been carried out to explore the conditions at whichchlorine dioxide is explosive. At ambient temperature, chlorine dioxidedoes not explode below 9.5% in air by volume. Above this limit,spontaneous explosive decomposition is noticed with an induction time.Induction time decreases as the concentration of chlorine dioxideincreases. Based on these one can plot the tendency to decompose as afunction of % chlorine dioxide in air. (FIG. 1)

Regarding FIG. 2: a) the hashed area is a recommended environment forgas storage—an environment with minimal decomposition, if it isnecessary to store the gas (for short or longer terms); b) the transportbetween chlorine dioxide generator and reaction vessel is deliberatelyshort and never obstructed, therefore requiring just seconds at most; c)as noted above, the contemplated NOx reaction only requires 1.5 secondsso from an induction time perspective the reaction chamber temperaturecould be elevated as long as the total partial pressure remained low;and d) as a reference point a 10% chlorine dioxide concentration in gasphase described in FIG. 1 corresponds to a partial pressure of 76 mm ofHg in FIG. 2—a value that is outside the safe working environmentdescribed in this chart. However, 5% chlorine dioxide in gas phasedescribed in FIG. 1 is well within the safe environment described onFIG. 2.

FIG. 3 shows that gas phase chlorine dioxide is theoretically safe at upto 9.5% (95,000 ppm(g)) when used in environments that effectivelyaddress all variables that affect decomposition. The safe concentrationfor chlorine gas dissolved in water varies dramatically withtemperature. By way of examples, which are referenced by the arrows inthe above graph, some pulp and paper operations safely store thousandsof gallons of chlorine dioxide dissolved in water near 9000 ppmconcentrations as long as it is maintained at near freezingtemperatures; chlorine dioxide is considered safe for transportation andgeneral storage at concentrations of 3000 ppm. This generalization istrue as long as the liquid is stored at or below 86° F.; and at 104° F.chlorine dioxide in water is safe at concentrations near 2200 ppm. Inaddition, there are other variables like sunlight and vibration thatinfluence chlorine dioxide decomposition which need to be considered inprocess design and chemical storage decisions.

As mentioned earlier, some embodiments allow for the ClO₂ gas to bedissolved in an aqueous solution with pH above 9. In these embodiments,the basic solution increases the scrubbing removal efficiency byproviding enhanced solubility for NOx. The basic solution, however,might be disadvantageous in embodiments where HCl and HNO₃ acids in thecondensate are being captured for commercial value.

In some embodiments, the rate of ClO₂ addition is based on theconcentration of NOx in the waste gas. In applications where the NOxconcentration is not consistent in the waste gas, then the addition ofautomated chemical feed controls may be utilized to optimize bothremoval efficiency and scrubber operating costs. An example ofcontemplated automated chemical feed controls is shown in Example 3.Contemplated automated feed controls are designed to sense the NOxconcentration in the treated waste gas and the liquid condensate pH thenadjust the amount of chlorine dioxide and basic liquid (if used) thatare sprayed into the waste gas.

A second mist or packed bed scrubbing stage is optional, and in someembodiments, may improve the decontaminated gas quality while enhancingthe capture of HCl and HNO₃. As mentioned earlier, the design of thereaction vessels is an important consideration in order to avoid theformation of submicron HCl droplets. Mist eliminators can aid in theremoval of this condition if droplets are allowed to form.

NOx-containing gas (waste gas, gas or waste air) may be streamed throughthe reaction vessel using a blower to move the air through the vessel.This blower can be placed before or after the vessel (upstream,midstream, or downstream of the vessel). In some embodiments, the bloweris placed downstream (after), because that placement keeps the ductingand vessel at slightly negative pressure when compared to theatmosphere, thereby eliminating the release of untreated air in theevent of a leak. The downstream orientation can be advantageous foranother reason—it reduces the pressure in the reaction system slightlybelow ambient. The lower working pressure enhances the safe workingenvironment for ClO₂. A variable frequency drive enhances operationalflexibility by allowing the air flow to be reduced during off hourswhile still maintaining a minimal number of air changes in the processareas that create the waste gas.

EXAMPLES Example 1 Exemplary Process and Apparatus

A process for NOx scrubbing, as disclosed herein, is demonstrated inthis Example by using a single stage pilot scale mist scrubber. Thepilot scrubber processed a slip stream of waste gas at approximately 22°C. from a chemical milling operation. The NOx concentration in the wastegas stream varied between 10 and 100 ppm during the series of testscompleted to prove up this new process methodology; however, it arepreferably understood that significant concentrations of NOx can betreated in a waste gas stream, including concentrations of about 20000ppm or more. The NO/NO₂ ratios in the NOx varied slightly however the NOconcentration was consistently above 90%.

FIG. 4 shows a section cut through a contemplated embodiment—the singlestage pilot scrubber—used in the performance testing. A scrubber vessel10 is PVC pipe mounted horizontally during testing. The vessel 10 in anyother configuration and orientation that can provide an enclosure formist is applicable and included in this description. Waste gas entersthe vessel 10 through a PVC pipe 11. A PVC baffle plate 12 disturbs thegas flow linearity in the vessel 10 prior to a gas swirling device 13.An air atomized nozzle (nozzle) 14 was used in tests to introduce gasand/or liquid to the waste gas stream in the vessel 10. In some teststhe nozzle 14 was used to introduce liquids through a tube 15 in othertest only gas was introduced to the nozzle through a tube 16. Thepressure and flow rate of gas fed to the nozzle 14 were adjusted at aregulator 17. A hole 20 was used to extract treated gas samples from thevessel 10. The hole 20 was repeated in the vessel 10 at intervals awayfrom the nozzle 14 so that samples with progressively longer residencetime in the vessel 10 could be obtained and analyzed to determine therate of NOx destruction in the gas within the vessel 10. The rate of NOxdestruction in the vessel 10 was determined by comparing the treated gassamples from the various hole 20 locations against untreated waste gassamples takes at a hole 21. Gas was moved through the vessel 10 byducting 22 connected to the suction side of a variable flow rate blower.

Contemplated processes, as outlined earlier, utilize two methods inwhich chlorine dioxide gas effectively converts gas containing both NOand NO₂ into HCl and HNO₃ in a single stage mist type gas scrubbingapparatus. The first method: reactions between gas containing NOx andchlorine dioxide gas dissolved in a basic solution (preferably above pH9). The second method: reactions between waste gas with high relativehumidity containing NOx and chlorine dioxide gas. Both reactions couldoccur according to the paths described in equation 32 and 33 below. Bothof these methods using single stage mist scrubbing apparatus are a majordeparture from the multi-stage wet scrubbing apparatus reported in priorart.

5NO+2ClO₂+H₂O→5NO₂+2HCl  (32)

5NO₂+ClO₂+3H₂O→5HNO₃+HCl  (33)

The overall rate of reaction for both equations 32 and 33 with greaterthan 99 removal efficiency is less than 1.5 seconds of residence timewhen the humid gas containing NOx and ClO₂ gas are well mixed.

An optional second stage mist or wet scrubbing apparatus can provideseveral functions. First it can remove of excess chlorine dioxide inapparatus that does not include automated controls to effectivelyregulate chlorine dioxide gas addition. Second, it can capture HCl andHNO₃ acid fumes in apparatus that introduces ClO₂ as a gas that is notdissolved in a basic solution.

The reactions described in equations 32 and 33 above occur more rapidlyin the mist and gas phase scrubbing technology than the wet scrubbingreactions described in equations 30 and 31 in the background section.The increased speed of reaction reduces the reaction vessel sizerequired for conversion of NOx to acids. Furthermore, the air or mistscrubbing methodology is less complicated and requires less maintenancethan packed bed or tray type wet scrubbers. As a result the air or misttechnology equipment is less expensive to purchase and operate.

Gas analysis for NO and NOx was done during the pilot testing withelectrochemical sensors for NO and NOx. These sensors were evaluated forcross sensitivity by other compounds known to be in the gas stream orsuspected of being present in the gas stream and also factory calibratedbefore and after testing. The electrochemical analysis was further crosschecked with EPA Method 07 for NOx.

Example 2 Form of Chlorine Dioxide Gas Introduction

Chlorine dioxide gas can be introduced to NOx and/or SOx in at leastthree ways: as a gas, as a mist and as a liquid. These three methods usethe same stoichiometry, because it is the ClO₂ gas that is reacting withthe NOx as opposed to an ionic form of chlorine dioxide in all threereactive environments, which is a major distinction between this processand others that have utilized the ionic variation of this molecule forwet scrubbing in the past.

The gas and mist phase systems have different mechanical configurations.In addition to different nozzle types, which is described in eachsection below, the sequence of mixing, along with ClO₂ addition, may bedifferent. Research has shown that mixing after gas injection worksbetter than the opposite in some embodiments, so in the gas phase thisis the sequence used, however, in other embodiments other configurationscan be employed. The issue of droplet aggregation may supersede thisadvantage in the mist systems. The mixing tends to cause agglomeration.Therefore where mist is used the mixing is usually introduced prior toClO₂ addition.

This contemplated application is ideal for operations with modest wastegas flow rates and modest NOx and/or SOx concentrations. The boundariesare flexible, but can be cost effective for waste gas flow rates ofabout 10,000 CFM or less and NOx concentrations of about 1000 or less.Higher concentrations of NOx and/or SOx can be treated, e.g., byincreasing the concentration of ClO₂, or by diluting the concentrationof NOx and/or SOx.

This process can be cost effective for smaller applications, becausethere is no need for the cost of onsite ClO₂ generation. ClO₂ gas can besupplied that has been suspended in water that is buffered to minimizeoff-gassing.

The ClO₂ can be introduced before, during and/or after the waste gas isswirled. Research has shown that air atomized nozzles are particularlywell-suited for this application. These produce fine mist droplets outof ClO₂ gas suspended in an aqueous phase. The goal is to maximize theratio of droplet surface area to liquid volume, which is achieved whenthe droplets are in the micron or sub-micron range. Although smaller istypically better, a desirable balance between performance and cost canbe found when the mean diameter is about 100 microns.

This is generally commercially available up to about 3,000 ppm ClO₂.Higher concentrations are possible at lower temperatures, but the needfor refrigeration introduces a safety concern in the event therefrigeration system fails. If appropriate systems are developed toaddress these safety concerns, then concentrations can be increasedaccordingly. This process generally requires about 1.5 seconds ofresidence time for 99% removal. Higher removal efficiency is possiblewith longer residence time.

Chlorine dioxide, in the gas phase, is introduced into the waste gasbefore it is mixed. This application works for various sizes of NOxand/or SOx loading situations, but good cost effectiveness inapplications where the waste gas stream is in excess of about 10,000 CFMwith NOx loading of about 50 ppm or more. If cost concerns arealleviated, NOx loading can be effectively increased. Contemplatedprocesses can be applicable to NOx (and/or SOx) loading as high as50,000 ppm or more.

An amount of chlorine dioxide for reaction with SOx is similar to anamount required to react with an equivalent amount of NOx (on a molarbasis). In other words, the same amount of ClO₂ may be suitable to treat2 equivalents of NOx or 1 equivalent of NOx and 1 equivalent of SOx. Theamount of chlorine dioxide added to the waste gas can be adjusteddepending upon the composition of the waste gas. Sensors can be providedthat detect the amount of SOx and/or NOx in the untreated waste gas andthis information employed to determine an amount of chlorine dioxide tobe added to the untreated waste gas. However, it may be advantageous tomeasure SOx and/or NOx in the treated waste gas. This information canthen be used to adjust, e.g., continuously or intermittently, the amountof chlorine dioxide introduced into the untreated waste gas so as toachieve a target SOx and/or NOx concentration in the treated waste gas.This latter configuration can offer advantages in that high SOx and/orNOx concentrations as in untreated waste gas can cause premature sensorfailure. The lower SOx and/or NOx concentrations in the treated wastegas can substantially increase sensor life, permitting longeruninterrupted operation of the reactor.

Contemplated processes using the gas phase can employ the generation ofgas phase ClO₂ on site, which is preferably done using electrochemicalmethodology. Contemplated chemical methods of generating ClO₂ produceClO₂ suspended in a liquid that has high pH and impurities. Thesechemical processes also generate waste acid that can be treated. Thehigh pH (NaOH) and other waste products from electrochemical processescan be used in a second stage acid fume scrubber so there is no waste totreat or to dispose, thereby offering a significant environmentaladvantage.

This gas phase process is typically at least 10 times faster than themist process, as described above, such that shorter residence times canbe employed. Current research includes treating NOx in waste gas streamsmoving at 2500 feet per minute with 99% removal efficiency in less thanabout 5 feet of duct length (after the mixing section). Thisconsiderably fast gas phase reaction dramatically reduces the size ofthe reaction vessel or eliminates it completely.

Example 3 Contemplated Automated Chemical Feed Controls

Contemplated controllers are designed to handle the entire air scrubbingprocess for a 32,000 CFM NOx scrubber system and similar systems.Contemplated devices monitor and regulate the following components:First Stage NOx scrubber (using ClO₂); Second stage acid scrubber (usingNaOH and other effluent from the ClO₂ generator; Manage a ClO₂generator; Fans; Storage and packaging system for ClO₂ gas suspended inwater (hereinafter identified as liquid ClO₂.); Communication both localand remote.

Contemplated control systems also manage the attached equipment in twomodes of operation: designed to insure the attached equipment canreliably and effectively remove NOx from a waste gas stream in a waythat safely optimizes the efficiency of the reaction between NaClO₂ andelectricity to form ClO₂ and optimizes the reaction between ClO₂ and NOxin the first scrubbing stage. Furthermore this system can insure gasleaving the second scrubbing stage is free of excess ClO₂ and mineralacid fumes; and at times when there is no need for gas phase ClO₂, thenthe ClO₂ generator has the ability to produce liquid ClO₂ in a safe andreliable way.

This system is an integral part of maintain an effective system. If thisair treatment system is down, production stops because without it, thesystem is out of compliance with regulatory constraints. Because thissystem is critical to production, the control system includes sensorsand control logic that allows evaluation of the equipment and reportingof conditions that can lead to shutdowns before they occur. This allowsthe operators to take action and avoid a shutdown in most if not allsituations.

Therefore, this system design includes a detailed evaluation of the PLClogic for a ClO₂ generator to insure this device can reliably and safelydeliver ClO₂ in the two previously mentioned phases.

Example 4 Generalized Process Control Parameters

-   -   1. There can be password control on the program. This applies        both to access at the HMI and remote access.        -   a. Operator Level can have the ability to change process            set-points pertaining to NOx removal efficiency from the            first stage and second stage. The minimum and maximum pH            settings for the second stage.        -   b. Technician Level can have the ability to change PID loop            tuning variables, intervals for data averaging and other            similar variables plus those variables controlled on the            Operator Level.        -   c. Programming Level can have the ability to update program            code and everything else.    -   2. The program indicates three levels of alarm and this        information can be available both at the HMI and remotely.        -   a. Warning: This includes non-critical range low or high            levels for process equipment. For example low or high tank            levels, low or high pressures, temperatures or process            efficiency.        -   b. Problem: This includes all critical levels for            temperature, pressure, tank level and process efficiency.        -   c. Shutdown: A critical variable has exceeded its set-point            and the automatic equipment shutdown sequence has occurred.    -   The warning level alarm conditions can be disabled at a        Technical level password protected screen.    -   3. The program can have automatic startup and shutdown sequences        for both the liquid and gas phase ClO₂ operations. These        shutdowns are triggered either by the process shutdown alarm or        by pressing the emergency stop button. The restart after        automated or emergency shutdown requires the operator to remedy        any alarm conditions prior to proceeding. This restart can have        the option of using either the previous process variable set        points or the default set points. The HMI shows what variable        has triggered the alarm and recommend in order of likelihood,        one or more suggested operator activates to remedy the alarm. In        addition to display on the HMI, this information can be conveyed        by email to selected individuals who require or need        notification.    -   4. The program supports data logged in a discrete way        (controlled behind a technical level password protected screen.)        The data logging preferably has the ability to be remotely        downloaded in a safe way. If encryption is easily available,        that would be a plus.    -   5. The controller sends a 4-20 mA signal to the ClO₂ generator        that is used to regulate the rate of ClO₂ production by the        generator. The value of this signal (AO-1) can be determined by        comparing the analog inputs from two separate sensors: NOx and        ClO₂. Both sensors measure their respective process variables        from exhaust gas at a point after the second stage scrubber.        Both of the sensors convey analytical data that represents the        concentrations of their measured gas via loop powered 4-20 mA        signals. The controller provides 24V DC power to each gas        transmitter and the transmitter superimposes a 4-20 mA signal on        this loop.    -   6. The analog output AO-1 from the controller utilizes “if then”        logic that is based on the following parameters:        -   a. Analog data from the NOx (AI-1) and ClO₂ (AI-2) sensor            are independently averaged. The averaging period duration is            changed on a screen that is protected by the Technical Level            password.        -   b. There can be a set point for maximum ClO₂ in the waste            gas stream. This set point can be changed at the Technical            Level.        -   c. There can be a set point for the maximum NOx in the            exhaust gas. This can be changed at the Operator Level.        -   d. If there are no alarms (system is operating properly) and            both sensors are at no-detect then the first stage scrubbing            system is optimally tuned.        -   e. If the NOx sensor is at no-detect and the ClO₂ is            detecting then turn down the ClO₂ generation until the            reported averaged sensor value is less than the set point            for average NOx in the waste gas stream.        -   f. If the NOx sensor is reading above the average NOx set            point then increase the ClO₂ generator output until the NOx            level is below the average NOx set point.        -   g. If both the ClO₂ and NOx are above their average set            points then the ClO₂ generation is rapidly increased            (accelerated PID ramp up rate) and a warning alarm is            triggered. This alarm automatically resets when the            condition is resolved.    -   7. The controller sends a 4-20 mA signal (AO-2) to the DP ClO₂        generator tank identified as 5-53-TK. (NaOH) metering pump. The        pH sensors convey their measured variable via loop powered 4-20        mA signals. The controller provides 24V DC power to the pH        transmitter and the transmitter superimposes a 4-20 mA signal on        this loop.        -   a. This metering pump can be connected to the discharge            point in the waste tank 5-53-TK.        -   b. It is recommended that the tank's 5-55-TK size to be            increased to 300 gallons or larger.        -   c. Waste RO water should go directly to a drain rather than            be included with the catholyte and analyte waste streams.        -   d. See #9-11 below for more information pertaining to tank            5-55-TK.    -   8. The controller sends a 4-20 mA signal (AO-3) to the sodium        hydroxide (NaOH) metering pump. The pH sensors convey their        measured variable via loop powered 4-20 mA signals. The        controller provides 24V DC power to the pH transmitter and the        transmitter superimposes a 4-20 mA signal on this loop.        -   a. This metering pump can be connected to a source of 50%            sodium hydroxide solution.    -   9. The pH set point of the second stage scrubber sump can be        maintained by utilizing a combination of both sodium hydroxide        sources.        -   a. The generator tank 5-53-TK can be used first.        -   b. If this pump is operating at full capacity and the pH set            point is still not met then the second chemical metering            pump connected to the 50% NaOH can be progressively            increased until the set point is reached.    -   10. Three digital sensors are preferably installed on the ClO₂        generator cell waste liquid tank (5-53-TK) a low, a medium-high        and high-high.        -   a. The PLC utilizes the low and the medium high to regulate            waste transfer pump 5-55-PU. This liquid is preferably            transferred to another location.        -   b. The PLC utilizes the high-high as part of the “problem”            level alarm condition logic.    -   11. A second discharge port is preferably installed from tank        5-53-TK. This can be made available to a chemical metering pump        supplied as part of the equipment. This fitting can have a        manual shut off valve and ½″ NPT fitting.    -   12. There can be a digital level sensor on the external liquid        ClO₂ tank. When this level is reached the ClO₂ generator is shut        off and shutdown alarm is triggered. This tank is not used        initially so the contact can be bypasses.    -   13. Ideally the generator preferably has the ability to control        concentration of ClO₂ being delivered in gas phase by two        methods:        -   a. Changing the power to the cells.        -   b. Changing the rate of gas flowing through the cell or            diverting a percentage of the ClO₂ laden gas into a bubbler            that stores it in water. The second activity improves the            speed of process control and minimize over or under feeding            ClO₂ into the first stage scrubber.    -   14. The generator sends the following digital signals to the        controller. All signals can be 24 volt DC and loop powered from        the control panel:        -   a. The generator is on and operating in the gas phase ClO₂            methodology (DI-1)        -   b. The generator is on and operating in the liquid phase            ClO₂ methodology (DI-2)        -   c. There is a Warning level alarm. Alarms that are in this            category can be defined (DI-3).        -   d. There is a Problem level alarm. Alarms that are in this            category can be defined (DI-4).        -   e. The generator is shutting down due to a shutdown level            alarm condition (DI-5).        -   f. The generator is shutting down due to manual command            (DI-6).        -   g. Once the available analog and digital data generated in            the Generator/PLC then some of these may be sent to the            controller as inputs.    -   15. Each process variable can be graphically displayed next to a        comparable bar chart that shows the set point for that variable.

Example 6 Process Details for First Stage (NOx Scrubber) and ClO₂Generator

Waste gas with varying concentrations of NO and NO₂ at temperaturesbetween 70 and 90 Fahrenheit and 30 to 80 percent relative humidity iseffectively mixed with ClO₂ gas in concentrations necessary to convertan operator determined percent of the NOx in the waste gas into mineralacids. Typically the removal efficiency is near 99.5 percent.

The ClO₂ gas injection rate into the waste gas varies according to ifthen logic described above.

A loop powered analog pressure sensor in the ClO₂ gas duct (AI-5). Twolevels of alarm are provided. The lower level can be a problem and thehigher triggers a generator shut down (DO-1). The pressure set pointscan be adjusted with Technical Level access.

Waste gas from the first stage with acid fumes and low or noconcentrations of NOx is treated in the existing counter current packedbed scrubber. The goal is to keep the pH as low as possible and stillmeet the NOx treatment set point. The pH is controlled by the additionof waste streams liquid from the generator and the addition of 50%sodium hydroxide liquid. All liquids can be introduced directly into thescrubber sump as described in #7-9 above.

Cleaning follows a policy of draining and re-filling the scrubber sumptwice per week and manually maintaining the scrubber liquid levelbetween water changes. Provide normally closed input (DI-8) in the eventa sump water level sensor is included for sump water level.

The recirculation pumps for the second stage scrubber are necessary inthis embodiment. The transmitters are manual at this time and areexpected to remain manual so there is no need to include inputs fromautomated alarms.

There are two fans associated with this contemplated scrubber. One ison/off and the other is controlled with a variable frequency drive. Itis essential that air is moving through the ducting while ClO₂ is beingintroduced to the waste gas. Therefore a gas flow sensors is required.

A normally closed gas flow sensor (DI-10) can be installed in the wastegas stream after the second stage. If this does not indicate gas flowwhen at least one fan is on then a Shutdown level alarm is immediatelytriggered. There can be a 10 second delay after fan start before thisalarm condition becomes active.

Example 7 I/O Table for PRDD Controller

ANALOG AI-1 NOx #1 gas concentration in post second stage waste gas.AI-2 ClO₂ gas concentration in post second stage waste gas. AI-3 The pHin the second stage scrubber sump. AI-4 AI-5 AO -1 ClO₂ Production ratecontrol for DP generator associated with first scrubbing stage AO-2 NaOHaddition from DP tank 5-53-TK to second scrubbing stage sump. AO-3 NaOHaddition from 50% NaOH tote to second scrubbing stage sump.

DIGITAL DI -1 The DP generator is on and operating in the gas phase ClO₂mode. DI-2 The DP generator is on and operating in the liquid phase ClO₂mode. DI-3 Warning level alarm from the DP generator DI-4 Problem levelalarm from the DP generator DI-5 Automatic shutdown of the DP generatordue to a shutdown alarm condition. DI-6 Manual shut down of the DPgenerator. DI-7 Low second stage sump water level. DI-8 Highdifferential pressure in second stage mist eliminator DI-9 Highdifferential pressure in the second stage scrubber DI-10 Low waste airflow in scrubbing duct system DI-11 High liquid ClO₂ tank sensor DO-1Shutdown command to the DP generator

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive. Thedisclosure is not limited to the disclosed embodiments. Variations tothe disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the claimed disclosure, from a study ofthe drawings, the disclosure and the appended claims.

All references cited herein are incorporated herein by reference intheir entirety. To the extent publications and patents or patentapplications incorporated by reference contradict the disclosurecontained in the specification, the specification is intended tosupersede and/or take precedence over any such contradictory material.

Unless otherwise defined, all terms (including technical and scientificterms) are to be given their ordinary and customary meaning to a personof ordinary skill in the art, and are not to be limited to a special orcustomized meaning unless expressly so defined herein. It are preferablynoted that the use of particular terminology when describing certainfeatures or aspects of the disclosure should not be taken to imply thatthe terminology is being re-defined herein to be restricted to includeany specific characteristics of the features or aspects of thedisclosure with which that terminology is associated. Terms and phrasesused in this application, and variations thereof, especially in theappended claims, unless otherwise expressly stated, are preferablyconstrued as open ended as opposed to limiting. As examples of theforegoing, the term ‘including’ are preferably read to mean ‘including,without limitation,’ ‘including but not limited to,’ or the like; theterm ‘comprising’ as used herein is synonymous with ‘including,’‘containing,’ or ‘characterized by,’ and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps; theterm ‘having’ are preferably interpreted as ‘having at least;’ the term‘includes’ are preferably interpreted as ‘includes but is not limitedto;’ the term ‘example’ is used to provide exemplary instances of theitem in discussion, not an exhaustive or limiting list thereof;adjectives such as ‘known’, ‘normal’, ‘standard’, and terms of similarmeaning should not be construed as limiting the item described to agiven time period or to an item available as of a given time, butinstead are preferably read to encompass known, normal, or standardtechnologies that may be available or known now or at any time in thefuture; and use of terms like ‘preferably,’ ‘preferred’, ‘desired,’ or‘desirable,’ and words of similar meaning should not be understood asimplying that certain features are critical, essential, or evenimportant to the structure or function of the invention, but instead asmerely intended to highlight alternative or additional features that mayor may not be utilized in a particular embodiment of the invention.Likewise, a group of items linked with the conjunction ‘and’ should notbe read as requiring that each and every one of those items be presentin the grouping, but rather are preferably read as ‘and/or’ unlessexpressly stated otherwise. Similarly, a group of items linked with theconjunction ‘or’ should not be read as requiring mutual exclusivityamong that group, but rather are preferably read as ‘and/or’ unlessexpressly stated otherwise.

Where a range of values is provided, it is understood that the upper andlower limit, and each intervening value between the upper and lowerlimit of the range is encompassed within the embodiments.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity. The indefinite article “a” or “an” does not exclude aplurality. A single processor or other unit may fulfill the functions ofseveral items recited in the claims. The mere fact that certain measuresare recited in mutually different dependent claims does not indicatethat a combination of these measures cannot be used to advantage. Anyreference signs in the claims should not be construed as limiting thescope.

It is further understood by those within the art that if a specificnumber of an introduced claim recitation is intended, such an intent isexplicitly recited in the claim, and in the absence of such recitationno such intent is present. For example, as an aid to understanding, thefollowing appended claims may contain usage of the introductory phrases“at least one” and “one or more” to introduce claim recitations.However, the use of such phrases should not be construed to imply thatthe introduction of a claim recitation by the indefinite articles “a” or“an” limits any particular claim containing such introduced claimrecitation to embodiments containing only one such recitation, even whenthe same claim includes the introductory phrases “one or more” or “atleast one” and indefinite articles such as “a” or “an” (e.g., “a” and/or“an” should typically be interpreted to mean “at least one” or “one ormore”); the same holds true for the use of definite articles used tointroduce claim recitations. In addition, even if a specific number ofan introduced claim recitation is explicitly recited, those skilled inthe art will recognize that such recitation should typically beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, typicallymeans at least two recitations, or two or more recitations).Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). In those instances where a conventionanalogous to “at least one of A, B, or C, etc.” is used, in general sucha construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, or C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It is further understoodby those within the art that virtually any disjunctive word and/orphrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, are preferably understood tocontemplate the possibilities of including one of the terms, either ofthe terms, or both terms. For example, the phrase “A or B” is understoodto include the possibilities of “A” or “B” or “A and B.”

All numbers expressing quantities of ingredients, reaction conditions,and so forth used in the specification are to be understood as beingmodified in all instances by the term ‘about.’ Accordingly, unlessindicated to the contrary, the numerical parameters set forth herein areapproximations that may vary depending upon the desired propertiessought to be obtained. At the very least, and not as an attempt to limitthe application of the doctrine of equivalents to the scope of anyclaims in any application claiming priority to the present application,each numerical parameter are preferably construed in light of the numberof significant digits and ordinary rounding approaches.

Furthermore, although the foregoing has been described in some detail byway of illustrations and examples for purposes of clarity andunderstanding, it is apparent to those skilled in the art that certainchanges and modifications may be practiced. Therefore, the descriptionand examples should not be construed as limiting the scope of theinvention to the specific embodiments and examples described herein, butrather to also cover all modification and alternatives coming with thetrue scope and spirit of the invention.

1. A method for scrubbing a waste gas, comprising, introducing into areaction vessel a waste gas containing at least one component selectedfrom the group consisting of a sulfur oxide and a nitrogen oxide;introducing chlorine dioxide into the reaction vessel; introducingturbulence into a mixture of the waste gas and the chlorine dioxide,whereby the chlorine dioxide reacts with the component, such that thecomponent is converted into at least one other compound, molecule oratom.
 2. The method of claim 1, wherein the chlorine dioxide is ingaseous form.
 3. The method of claim 1, wherein the chlorine dioxidereacts with the component under conditions of ambient temperature andambient humidity.
 4. The method of claim 1, wherein the chlorine dioxideis introduced into the reaction vessel via at least one introductionduct.
 5. The method of claim 1, wherein turbulence is introduced bypassing at least one of the waste gas and the chlorine dioxide through aset of two or more blades in a fan configuration.
 6. The method of claim1, wherein turbulence is introduced by passing at least one of the wastegas and the chlorine dioxide through a plurality of tubes arranged in aparallel configuration, wherein each tube is positioned at an angle offrom 5 to 95 degrees off an axis of the reaction vessel, and whereineach tube is less than 0.5 meters in length.
 7. The method of claim 1,wherein the mixture is passed through two or more reaction vesselsarranged in series.
 8. The method of claim 1, wherein a sensor fordetection of at least one of the component, compound, molecule, or atomis positioned at an exit from the reaction vessel, and wherein ameasurement by the sensor is employed to adjust an amount of at leastone of the waste gas and chlorine dioxide in the mixture so as toincrease a rate and/or an amount of reaction of the component.
 9. Themethod of claim 1, wherein a residence time of the mixture in thereactor is 1.5 seconds or less, and wherein a conversion of thecomponent of at least 99% is achieved.
 10. A system for scrubbing awaste gas of at least one of nitrogen oxides and sulfur oxides,comprising: an inlet for introducing chlorine dioxide into the reactionvessel; and an inlet for introducing waste gas into the reaction vessel;and a reaction vessel, wherein the reaction vessel is equipped with oneor more turbulence inducing devices for inducing turbulence in a mixtureof the waste gas and the chlorine dioxide.
 11. The system of claim 10,further comprising at least one sensor positioned in an outlet of thereaction vessel, wherein the sensor is configured to measure at leastone of sulfur oxide, nitrogen oxide, water, or temperature.
 12. Thesystem of claim 10, wherein the reaction vessel is configured such thata residence time of a 1.5 seconds or less.
 13. The system of claim 10,wherein the turbulence inducing device is selected from the groupconsisting of vanes, baffles, diffusers, and tube arrays.
 14. The systemof claim 10, further comprising at least one additional reaction vessel,wherein the reaction vessels are arranged in series.
 15. The system ofclaim 10, wherein a gas velocity of the mixture is less than about 2500feet per minute
 16. (canceled)
 17. A method comprising: contacting afirst stream comprising NO and/or NO₂ (NO_(x)) with a second stream toconvert the NO_(x) in the first stream to one or more mineral acidsand/or salts thereof in a single-stage conversion, wherein: the secondstream comprises nonionic gas phase chlorine dioxide) ((ClO₂)⁰) andwherein the contact time of the first and the second streams is about3.0 seconds or shorter.
 18. A method comprising: contacting a firststream comprising NO and/or NO₂ (NO_(x)) with a second stream to convertthe NO_(x) in the first stream to nitric acid and/or salts thereof in asingle-stage conversion, wherein: the second stream comprises a gasstream comprising (ClO₂)⁰ gas and a mist stream, a liquid stream or acombination thereof, and wherein the contact time of the first and thesecond streams is about 3.0 seconds or shorter.